iio: pressure: bmp280: Fix alignment for DMA safety

Adds DMA-safe buffers to driver data struct to store raw data from sensors

The multiple buffers used thorough the driver share the same memory
allocated as part of the device data instance. The union containing
the buffers is aligned to allow safe usage with DMA operations, such
as regmap bulk read calls.

Updated measurement and calibration reading functions to use the safe
DMA buffers.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Angel Iglesias <ang.iglesiasg@gmail.com>
Link: https://lore.kernel.org/r/7919793f7f63224d5ce413c66d648029683c17ac.1663025017.git.ang.iglesiasg@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>